Smithboro till of Jacobs and Lineback (1969) is here proposed as Smithboro Till Member of Glasford Formation. It is the lowest till member of the Glasford in south-central IL and may be equivalent to the Kellerville Till Member in western IL, though their compositions differ slightly. The Smithboro is more silty than the Vandalia Till and is higher in expandable clay mineral content. Underlies the Mulberry Grove Silt at the type section. Age is Pleistocene (Illinoian).

Source: GNU records (USGS DDS-6; Reston GNULEX).

Smithboro Till Member is one of four members of Glasford Formation present in the study area. At the Martinsville alternative site, the Smithboro is composed of silt loam to loam diamicton and commonly contains wood fragments and sparse gastropod shells. Composed chiefly of diamicton, but layers of sand and gravel were encountered in several borings. The mineralogy of the fine grained sand fraction indicates that the Smithboro was deposited by the Lake Michigan Lobe of the Laurentide Ice Sheet. Unit is not exposed at the ground surface at Martinsville but is as much as 97 ft thick in the bedrock valley. Mean thickness is 28 ft in the study area. Elsewhere, unit does not exceed 10 ft. Truncates the Petersburg Silt and Martinsville sand at several localities. Underlies Vandalia Till Member. Age is Pleistocene (Illinoian).

Source: GNU records (USGS DDS-6; Reston GNULEX).